Hydraulic brake



April l14, 1936. E. F. LowEKE HYDRAULIC BRAKE Filed Jan. 25 1929 ww/22m Patented. Apr. 14, 1936 UNITED STATES PATENT OFFICE draulic ,Brake Company,

poration of California 3 Claims.

my Invention relates to a hydraulic brake system and m re particularly to an improvement in the mast r cylinder lor a hydraulic brake system.

One of the problems encountered in a hydraulic brake system is to provide means for effectively preventingair from entering the system i'or the reason that air being high compressible detrimentally affects the operation of the system. In those types of hydraulic brake systems in which the master cylinder is not submerged in the brake iluid the most diflicult point at which to seal the system against the admission of air has been at the piston which is engaged at its rear side by the piston actuating mechanism.

An object of the .invention is to provide an improved hydraulic brake system.

A further object is to provide a master cylinder having means for preventing the admission of air into the cylinder.

A further object is to provide a master cylinder having means for sealing theA piston from, the atmosphere and at the same time subjecting the rear side of the piston to atmospheric pressure.

A further object is to provide an improved means for actuating the piston ci the master cylinder.

Other objects and advantages will appear as the description proceeds.

In accordance with'the general features of the invention, a movable piston is mounted in the master cylinder and a ilexible boot encloses the end of the cylinder and the rear side of the pisl pressure.

Referring to the drawing: Fig. 1 is a longitudinal section of the master cylinder assembly, and i Fig. 2 is a schematic View of the master cylinder and the Wheel brake cylinders, illustrating the manner of connecting the wheel brake cylinders to the master cylinder.

The invention comprises, in general, a fluid reservoir II, master cylinder I2 and wheel brake cylinders I3. The master cylinder has a piston I4 reciprbcably mounted therein. The piston comprises a face portion I5 adapted to carry a packing cup I 6 and a rearwardly extending ilange I 1 spaced from thecylinder wall. The end of the rearwardly extending iiange I1 has a radial flange I8 which contacts with the cylinder wall to guide the piston in the cylinder, forming an annular recess I9 around the piston.

Detroit, Mich.; a cor- Aispucaaon .Imam ze, 1929, serial mi; 335,285

(ol. stl-'54s) A ring 22 is retained ni the end of the cylinder by a split ring 23 and is adapted to limit the rearward movement of the piston. The piston is also provided with a socket 24 which engages a ball 25 of a plunger 26 by means of which the piston may be moved. Plunger 26 is provided at its opposite end with an annular ring 21 having an under cut shoulder 26. 'I'he end 29 of the plunger is threaded and is adapted to receive a nut 32 having a similar undercut shoulder 33. 10

' Shoulders 28 and 33 are adapted to engage the annular beaded end of a boot 34 ofrubber or any other suitable material which surrounds the plunger. The iront end of the boot is formed into a radial extending flange 35 which is held against 15 the cylinder by a'ring 36. lRing 36 has a cylindrical portion 31 integral therewith `and extending rearwardly, which is provided at its end with" Y vehicles. A suitable material for this purpose.- isgimpregnated airplane cloth or leather. Boot 42g() thus serves to protect the ilexible boot 34 from oils a; and dust and other matter which might be in-v.l jurious thereto. Boot 42 is provided at its lower side with an aperture 45 connecting the interior o! the boot with the atmosphere. 35

'I'he rearwardly extending iiange I 1 of the piston is provided with apertures 46, and the wall oi' cylinder I2 is provided with an aperture 41 leading into the space 48 which is in communication through a tube 49 with the iluid reservoir. 40 Thus iluid from the reservoir passes through tube 49, space 48, the aperture 41 into thel annular recess I 9 of the piston and through passages 46 in the piston into the flexible boot 34, which forms a fluid chamber enclosing the rear side of the piston.

The face of the piston is provided with a plurality of passages 5I which extend into the space in the cylinder. During the forward movement of the piston these passages are covered by the 50 packing cup I6 causing a. iiuid pressure to be produced in the master cylinder.

At the discharge end ot the cylinder is a valve comprising a resilient cup-shaped valve member i2 adapted to rest against the valve seat formed 55 by the end of the cylinder wall. Surrounding the resilient member. 52 is a cup-shaped rigid valve member 53 having a radially extending annular ange 54. A spring 55 is interposed between the piston and the valve resting at one end against a Washer 56 engaging the packing cup I6 and at the other end against the annular flange of the rigid valve member 53, urging this member forward and yieldingly retaining the resilient member 52 against its seat. The yielding valve member 52 is provided with a plurality of apertures 51 and the rigid valve member 53 is provided Witha central aperture 58.

As the piston I4 moves forwardly producing a fluid pressure in the cylinder, fluid passes through aperture 58 forcing the central portion of the yielding valve member 52 away from the rigid valve member and allowing the fluid to pass through apertures 51 to the wheel brake cylinders to apply the brakes.

Plunger 26 is provided with a cylindrical bore 6l into which a connecting rod 62 pivotally attached to the end of pedal 63 projects. This construction causes the depression of the pedal to produce a. positive movement of the piston in its forward direction. However, upon release of the pedal and its return to its normal position, the piston will not be positively withdrawn but instead connecting rod 62 will be withdrawn from plunger 26, the retraction of the piston being caused by spring 55. During the retraction of the piston the valve in the end of the cylinder will be yieldingly urged to its seat by the spring to maintain a positive pressure in the wheel brake cylinder and the iluid lines leading thereto.

The amount of positive pressure in the wheel brake cylinders will depend upon the relative sizes of the valve andthe piston. Since the rear side of the piston is subjected to atmospheric pressure, the valve may be made of such a. size as to maintain a p 'ressure of six pounds above atmospheric pressure in the wheel brake cylinders.

Retraction of the piston produces a. low pressure in the master cylinder, causing the packing cup to become unseated and allowing iluid from the rear side of the piston to pass through passages into the master cylinder.

It will be noted that it is impossible for a low pressure to be produced in the chamber formed by flexible boot 34 since any depletion of the liquid therein will merely cause a contraction of the bootcorresponding to the reduction in the volume of the boot without resulting in a low pressure therein. Furthermore, the fluid chamber formed by the boot is constantly in communication with'the uid reservoir to supply additional fluid thereto.

When the piston arrives in its retracted position there will be an excess o1' uid in the master cylinder due to the fact that the iluid w'lll continue to enter the cylinder from the wheel brake lcylinders after the piston is retracted. The excess uid which is present in the cylinder may escape through a passage 64 in the upper wall of the cylinder located immediately in front of the retracted position of the piston. Thus upon each application of the brakes an excess of fluid will be .provided in the master cylinder, due to alow pressure therein. However, the valve at the exit of the cylinder and the boot at the rear side of the piston enclosing the other end of the cylinder eiectively prevent the low pressure inthe master cylinder from extending to any point at which there is a. possibility of air being drawn into the brake system.

Having described the nature and embodiments .of my invention, what I claim and desire to secure by United States lows:

1. In a hydraulic brake system, a master cylinder, a piston movable therein and having an annular recess, a fluid reservoir communicating with said recess, and a. exible boot enclosing the end of thecylinder, said piston having an aperture interconnecting the boot with the annular recess and the reservoir.

2. In a hydraulic brake system, a master cylinder, a piston movable therein comprising a cylindrical portion having an annular recess and provided with an aperture through its wall, and a face portion having a passage therethrough connecting the cylinder with the interior of the piston, a boot enclosing the rearward end of the piston, a fluid reservoir communicating with the boot through the recess of the piston and with the cylinder at a point immediately in front of the retracted position of the piston, a packing cup carried by the piston face adapted to close the passage in the face of the piston during the compression stroke of the vpiston and uncover said passage in the retractile stroke to allow uid to enter the cylinder therethrough.

3. In a hydraulic brake system, a master cylinder, a piston reciprocable therein, a flexible boot forming a variable volume fluid chamber rearwardly of the piston, a. fluid reservoir, means establishing a fluid connection between the fluid chamber and the reservoir, means for moving the piston forwardlyv to produce a. uid pressure, securing means for the ilexible boot on the cylinder and the means for moving the piston, a valve at the forward end of the cylinder for Letters Patent is as folretarding the return of fluid to the cylinder,

means for retracting the piston producing a low pressure in the cylinder, and means for establishing a fluid communication between said chamber and the cylinder during the retractile movement of the piston allowing uid to enter the cylinder from said chamber, said cylinder having an aperture immediately in front of the i retracted position of the piston to allow excess iluid to escape from the cylinder. l

ERWIN F. LOWEKE. 

